1. Field of the Invention
The present invention relates to an electric heating treatment method, an electric heating treatment apparatus, and an electrode for the electric heating treatment apparatus, and more particularly, to an electric heating treatment method and an electric heating treatment apparatus for treating the surfaces of works by electrically heating the works.
2. Description of the Related Art
In general, the surfaces of the inter-valve sections of a cylinder head formed of aluminum alloy casting in a diesel engine, for example, are provided with remelting treatment to make them resistant to high thermal stress. Conventionally, the remelting treatment is carried out by applying high-density energy using a TIG arc, plasma arc, laser beam, electron beam, etc. For instance, in the case of the remelting treatment using an arc, as schematically shown in the sectional view of FIG. 35, a high temperature arc 42 is radiated from a torch 41 placed away by a predetermined distance from the surface of a work 40 to melt the surface of the work 40 by the heat transmitted from the arc 42. Then, the torch 41 is continuously moved along a portion requiring the remelting treatment. At this time, right beneath the arc 42, a new crater 45 is created by the arc 42, and the portion melted by the arc 42 flows to a portion that has been a crater 45a before the torch 41 was moved so as to fill the crater 45a; the portion is rapidly self-cooled due to the withdrawal of heat to a base material and it solidifies. As a result, the structure of the surface portion of the work 40 is turned into a continuous finer structure as the torch 41 is moved so as to produce a reinforced layer 46. A shielding gas 43 of argon, helium, or other gas is simultaneously sprayed from the torch 41 at around the arc 42 to prevent the melted portion from being oxidized due to contact with air.
It has been proposed to evenly heat a whole cam shaft by abutting electrodes against both ends of the cam shaft to perform preheating prior to the remelting treatment of the cam shaft as disclosed in, for example, Japanese Patent Publication No. 5-156346.
As disclosed in, for example, Japanese Patent Publication No. 6-172846, it has been known that a metal strip moved in a continuous heat treatment furnace is electrically heated by carbon roll electrodes to anneal it.
Further, it has been proposed in, for example, Japanese Patent Publication No. 64-56817, to abut an electrode against a part of a work and to form a bypass electric path for detouring a hot portion or the abutted portion of the work. Thus, when the portion other than the hot portion of the work reaches approximately the same temperature as the hot portion, the bypass electric path is released to electrically heat the whole work.
Furthermore, it has been known to electrically heat a metal strip moved in a continuous heat treatment furnace by carbon roll electrodes to anneal it as disclosed in, for example, Japanese Patent Publication No. 6-172846.